linux-kernel - Re: [PATCH] KVM: async_pf: Fix rcu_irq

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Message-ID: <CANRm+Cw4r5_d_ZO=xtEwXhA2UzZOH0mu6=T8AGHWAQx7N1uVOg@mail.gmail.com>
Date:   Wed, 7 Jun 2017 22:10:33 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: async_pf: Fix rcu_irq_enter/exit() usage

2017-06-07 21:05 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>
>
> On 07/06/2017 14:04, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault)
>> adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs
>> when needed, to protect the code that needs use rcu. There is no need to call
>> this pairs if async page fault is not triggered from idle task.
>>
>> This patch fixes it by rcu irq exit if it is not triggered from idle task to
>> avoid rcu hang after schedule() in the for loop.
>
> How does the bug manifest?

Just by codes review.

Regards,
Wanpeng Li